What should you look for in high temperature ice and water shield?
Short answer. High temperature ice and water shield is a self-adhered underlayment rated to stay stable at elevated service temperatures, often around 250 to 260 degrees Fahrenheit, for use under metal and other hot roof coverings. When comparing products, look for that in-service rating on the data sheet, separate from the application temperature range and the allowed UV exposure time.
The numbers on a data sheet, decoded
- In-service or thermal stability temperature. The heat the installed membrane can tolerate without flowing or sliding. This is the number that separates high temperature products from standard ones. As one example, a widely used standard membrane lists about 200 degrees, while its high temperature version lists about 260.
- Application temperature. The air and deck temperatures at which the membrane will stick when installed. This is about installation day, not long-term performance.
- UV exposure limit. How many days it can sit uncovered in sunlight. High temperature products often allow longer exposure, in the range of months, but check the specific product.
- Standard compliance. Look for ASTM D1970, the standard for self-adhering underlayments used under steep roofing.
- Surface type. Film, woven or granular. Granular surfaces give better footing; smooth films can be slick.
Questions to ask about your roof
- Does the metal panel manufacturer require a specific membrane or a slip sheet over it?
- Is the metal a dark color in full sun? Dark finishes run hotter.
- Will the membrane sit uncovered for a while because panels are on order?
- Does the membrane need a primer on the deck at cooler temperatures?
When you do not need it
Under standard asphalt shingles, a regular ASTM D1970 membrane is the norm, and many shingle makers specify their own leak barrier for system warranties. Paying for high temperature membrane under shingles is harmless but rarely necessary. Background in ice and water shield in Georgia and metal roofing in Georgia.